OBJECTIVE: In 1996 we found by serendipity that 2 patients with rheumatoid arthritis (RA) who were taking clarithromycin (CM) to eradicate Helicobacter pylori experienced a regression of their RA symptoms. Following this observation, we tested the hypothesis that this reduction in symptoms could have been caused by CM administration. METHODS: We performed a 6-month, open, uncontrolled pilot study on 18 patients (14 females and 4 males, mean age 62 yrs.) with RA who had previously received DMARDs (mean 2.6) and discontinued the treatment at least one month earlier because lack of efficacy or severe side effects. Patients were treated with CM at the dose of 500 mg twice per day for the first 10 days, followed by a daily maintenance dose of 250 mg twice per day. RESULTS: 4/18 patients did not complete the treatment, 2/18 were not responsive to the treatment and 2/18 discontinued the treatment. Following ACR criteria the improvement was: 10 patients ACR 20; 6 patients ACR 50; and 2 patients ACR 70. The remaining 4 patients did not reach ACR 20 since either the number of tender or swollen joints was not to the level required. Reductions in PGE2 and soluble phospholipase A2 plasma levels were closely related to CM plasma levels. CONCLUSIONS: Ourfindings suggest that CM treatment can be beneficial in those patients who are not responsive to or cannot tolerate DMARDs. No definitive conclusions can be drawn based on the present study, due to the small sample size involved.